Traveling to China to see giant pandas isn’t a trip you undertake lightly. Nor is exploring the Galapagos for 100-year-old tortoises or the Arctic for polar bears. But you can enjoy all these experiences in a single day at the San Diego Zoo.

Approximately 175 million people—half of America’s population—visit a zoo or aquarium each year, according to the AZA, a nonprofit accreditation organization. And more than 3.2 million choose the San Diego Zoo, making it the most popular in America. The appeal, according to Steve Feldman, spokesperson for the AZA, is natural: “People are hardwired to connect with other species and animals.”

In recent years, zoos have turned their attention to creating immersive exhibits that closely resemble the environments of wildlife-rich locales like the Serengeti or Madagascar—which ends up being a boon for both animals and their human guests. “Every zoo is trying to create habitats that replicate the wild,” affirms Jack Hanna, director emeritus of the Columbus Zoo and host of Jack Hanna’s Into the Wild.

At Minnesota Zoo’s Russia’s Grizzly Coast, for instance, visitors walk through a sea cave and past billowing steam vents, bubbling mud pots, and an erupting geyser before heading into a lava tube and coming face-to-face with giant brown bears.

The Denver Zoo, which comes in at No. 9, just opened the Toyota Elephant Passage this summer. Gibbons swing from vines overhead as guests look out for one-horned rhinos, Malayan tapirs, Asian small-clawed otters, and of course, stately Asian elephants in outdoor areas that look like they were transported from Thailand.

While such exhibits draw crowds, zoos also offer hundreds of special events that keep people coming back. “Brew at the Zoo” nights held across the U.S.—including Atlanta, D.C., Denver, and Phoenix—pair craft beer tasting with conservation fundraising. Around Halloween, a number of parks, including Columbus, Ohio, host “Boo at the Zoo” days, which feature haunted rides and opportunities to watch animals get their turn at smashing pumpkins.

Then there’s the money factor. Admission prices to most zoos are less than movie tickets, and sometimes free—notably at the No. 6–ranked National Zoo, home of famous giant pandas Tian Tian and Mei Xiang. If you purchase a membership to an AZA-accredited zoo, you can receive free or discounted admission at others (aza.org/reciprocity).

Ready to plan your visit? See which adorable zoo animals and cool attractions have drawn millions of people to the 20 most popular zoos in America.

The Methodology: We sourced our data from the Association of Zoos and Aquariums (AZA), which tracks annual attendance rates at accredited zoos in America (all major zoos are accredited). Attendance figures were reported by individual zoos. We used the numbers from 2010, the latest year for which comprehensive data were available. We did not include theme parks because they do not publicly report attendance rates and they have world-class thrill rides that are big draws in attracting visitors. (Had we chosen to include them, Disney’s Animal Kingdom would have been No. 1 and Busch Gardens Tampa Bay would have been No. 2, with respectively 9,686,000 and 4,200,000 annual guests.) Since our focus was on traditional zoos, we chose not to include aquariums, a category of their own. However, we did not exclude zoos that had an aquarium on their premises as part of the entire zoo.

1 of 20Courtesy of San Diego Zoo

No. 1 San Diego Zoo

Annual Visitors: 3.2 million

Balboa Park, which overlooks the Pacific, is the enviable—and accessible—setting for this world-famous 100-acre zoo. (San Diego Zoo Safari Park, 30 miles away, comes in at No. 19.) More than 3 million annual visitors flock here to see the 3,700-plus rare and endangered animals—first and foremost, the three giant pandas. Gao Gao, Bai Yun, and youngster Yun Zi (born in 2009) can be found noshing on bamboo and hanging around tree branches at the Panda Trek exhibit. Several Galapagos tortoises have called the zoo home since 1928, and at more than 100 years old, they’re the most senior citizens. In 2013, the zoo’s two dozen koalas will be upgraded to a spiffy new outdoor habitat.

No. 2 Lincoln Park Zoo, Chicago

Annual Visitors: 3 million

This Chicago zoo feels very much like a park within the city thanks to its location on the scenic shores of Lake Michigan. Visitors are free to stop in after a walk along Lake Shore Drive and wander around as they please—sans admission fee. Opened in June 2010, the stately new Nature Boardwalk offers opportunities to spot rare migratory birds, like black-crowned night herons, and take in unspoiled views of the Chicago skyline. You can see gorillas and chimpanzees up close at the $26 million Regenstein Center for African Apes, and pygmy hippos, dwarf crocodiles, and the zoo’s first red river hog at the 75,000-square-foot Regenstein African Journey.

No. 3 Saint Louis Zoo, MO

Annual Visitors: 2,934,753

The Saint Louis Zoo has the country’s most active AZA Species Survival Plans, which are long-term programs that help endangered species thrive—here, notably, a family of Asian elephants, Amur tigers, horned guans, and Chinese alligators. But that’s not to say more common animals can’t share the spotlight. Eleven lucky sea lions now live in $18 million digs at the new Sea Lion Sound. Visitors can watch the graceful mammals bask on rock ledges or swim overhead from a clear, 35-foot underwater tunnel, the first in North America.

No. 4 Columbus Zoo and Aquarium, OH

Annual Visitors: 2,374,125

You may recognize Jack Hanna from his wildlife TV series and talk show appearances, but you may not know that as Columbus Zoo’s long time director, and now director emeritus, he also modernized, expanded and transformed the park into the popular destination it is today. Among the zoo’s 10,000 animals are five generations of gorillas, including Colo, the first to be born in captivity, 55 years ago. At Polar Frontier, guests can see giant polar bears swimming overhead and catch playful brown bears digging in the ground. In 2014, the zoo will open the sprawling Safari Africa, where lions, zebras, and giraffes will roam over 50 acres of land resembling the Serengeti.

No. 5 Brookfield Zoo, IL

Annual Visitors: 2,283,065

Two thousand animals from approximately 400 species call this 216-acre zoo home. Managed by the Chicago Zoological Society, it was the site of the first indoor, multispecies exhibit and still has one of the world’s largest today: Tropic World houses primates from three continents. Spider monkeys scamper through the South American area, white-cheeked gibbons swing from tree to tree in the Asia section, and western lowland gorillas hold court over the African forest. Great Bear Wilderness, the zoo’s newest and largest exhibit, gives visitors a close look at animals they’d be more likely to find in a national park: grizzlies, bison, bald eagles, and Mexican gray wolves.

No. 6 Smithsonian National Zoological Park, D.C.

Annual Visitors: 2,251,712

Bo is the First Dog, but he’s not the only famous animal in town. Giant pandas Tian Tian and Mei Xiang are among the biggest draws for more than 2.2 million visitors who flock to the National Zoo each year. The adorable black-and-white bears share the Asia Trail area with six other species, including red pandas and fishing cats, which both welcomed babies in the past year. Fall 2012 will mark the opening of American Trail, a new habitat for seals and sea lions. And look for the completed expansion of Elephant Trails, where popular Asian elephants Shanthi, Kandula, and Ambika live, in Spring 2013.

No. 7 Como Park Zoo and Conservatory, St. Paul, MN

Annual Visitors: 2,230,000

Como Zoo’s Sparky the sea lion is so beloved that she has a statue in the park—and her own Facebook page. For more than 50 summers, millions of zoo-goers have attended Sparky shows to see the sea lion (and her like-named successors) catch balls and rings, imitate other zoo animals, jump, swim, and grin at the audience. Also popular is Polar Bear Odyssey, where the creatures swim, dig, and fish in a landscape that resembles their native tundra. Starting in 2013, it’ll be even easier for families to get up close to their primate cousins. The new Gorilla Forest will have a 10,000-square-foot outdoor area where the animals—plus five new gorillas—can climb, play, and just relax.

No. 8 Bronx Zoo, NY

Annual Visitors: 2,045,504

At 265 acres, NYC’s Bronx Zoo is America’s largest urban zoo. Yet, you feel miles away from the big city when you’re hanging with lemurs, mongooses, Nile crocodiles, and hissing cockroaches (whose roars can be as loud as a lawnmower) at the marquee Madagascar! exhibition. Zebras, giraffes, and of course, lions rule the African Plains, while more than 20 western lowland gorillas reside in the Congo Gorilla Forest. Little kids will love a ride on the Bug Carousel, a merry-go-round with grasshoppers, praying mantises, and other insects instead of horses.

No. 9 Denver Zoological Gardens

Annual Visitors: 1,967,839*

Gibbons swing overhead as visitors make their way to see Asian elephants swimming and walking in their spacious habitat, the $50 million, 10-acre Toyota Elephant Passage, opened in Summer 2012. One-horned rhinos, tapirs, fishing cats, and flying foxes also make their home in the exhibit’s outdoor areas. The zoo’s revamped black rhino and hippo abodes will be completed in late 2012.

No. 10 Houston Zoo

Annual Visitors: 1,841,777

The Houston Zoo invested $40 million in the 6.5-acre African Forest, where chimpanzees, white rhinos, cheetahs, and giraffes now roam. The exhibit features an elevated viewing platform where guests can feed heads of lettuce to giraffes. At the expanded McNair Asian Elephant Habitat, you can watch babies Baylor and Tupelo swim in a new 80,000-gallon pool. Aurora, a sweet one-year-old orangutan, also draws a crowd. Her mother rejected her at birth, and 50 zoo workers and volunteers tended to her for 10 months until she could be placed in the care of Cheyenne, her adoptive orangutan mom.

No. 11 Oregon Zoo, Portland

Annual Visitors: 1,645,843

Portlanders aren’t the only ones passionate about this zoo, whose annual attendance rate exceeds the area’s population. Much of that is due to the zoo’s legacy with elephants. The 1953 arrival of Rosy from Thailand spurred the construction of a new zoo, and in 1962, it was the site of the first elephant birth in the Western Hemisphere. Packy, now 50 and still at the park, is a local icon. New exhibits include Predators of the Serengeti (which features lions, cheetahs, and African wild dogs) and the Red Ape Reserve, where you’ll find orangutans and white-cheeked gibbons. The zoo also launched a 20-year plan to upgrade animal habitats to better resemble their native environments—in a sustainable way. (This is Portland, after all!)

No. 12 Los Angeles Zoo and Botanical Gardens

Annual Visitors: 1,500,000

Despite the presence of favorites like elephants and gorillas, scaly creatures and cold-blooded animals are among this zoo’s main attractions. The popular LAIR exhibition (Living Amphibians, Invertebrates, and Reptiles) houses Chinese giant salamanders, poison dart frogs, Gila monsters, and numerous poisonous snakes. The zoo also has a pair of Komodo dragons—the world’s largest lizard. Indigenous animals like giant otters, tapirs, primates, and harpy eagles will get their turn in the spotlight when Rainforest of the Americas opens in 2013.

No. 13 Omaha’s Henry Doorly Zoo and Aquarium, NE

Annual Visitors: 1,452,029

When you think of Omaha, the words hot, dry, and sandy probably don’t come to mind. Yet, thanks to the Omaha Zoo, the city is home to the world’s largest indoor desert. The Desert Dome transports guests to the Namib Desert, Australia’s Red Center, and the Sonoran Desert; cobras, meerkats, spiny iguanas, and peccaries are among the inhabitants. And that’s not the zoo’s only record-breaking attraction. Kingdoms of the Night is the world’s largest indoor nocturnal exhibit and indoor swamp. There, you can see bats, aardvarks, a Japanese giant salamander, and Parma wallabies out and about—since it’s nighttime to them. Monkeys, macaws, and pygmy hippos live in the Lied Jungle—which is also America’s largest indoor rainforest.

No. 14 Phoenix Zoo

Annual Visitors: 1,450,377

Only one cultural attraction in Arizona gets more visitors than the Phoenix Zoo—and that’s the Grand Canyon. Thanks to recent exhibit overhauls and openings, the zoo has even more ways to give the national landmark a run for its money. Bornean orangutans and a brother-sister pair of Komodo dragons now have slick new habitats to call home. At the 11-acre Savanna, you can spot a host of African animals, including Watusi cattle, giraffes, vultures, ostriches, and Thompson gazelles. Sci-fi geeks will appreciate Monkey Village: all of its 17 squirrel monkey inhabitants are named after Star Trek characters.

No. 15 Cincinnati Zoo & Botanical Garden, OH

Annual Visitors: 1,399,809

Feline fans have a new reason to head to America’s second-oldest zoo. At the Cat Canyon, visitors can now watch Malayan tigers, cougars, snow leopards, and white tigers bask on rocks and lounge among waterfalls. More wild kitties await at Night Hunters, a recently opened nocturnal exhibit. There, see sand cats, fishing cats, bobcats, and ocelots stalk about in darkened areas. Not a cat person? Not a problem. The zoo’s 500-plus species count everything from manatees to polar bears.

No. 16 Minnesota Zoological Garden, Apple Valley, MN

Annual Visitors: 1,338,581

At Russia’s Grizzly Coast, one of the Minnesota Zoo’s most popular exhibits, you can experience that country’s rugged wilderness without flying halfway around the world. Walk through a sea cave and catch otters swimming by. Then, stroll past billowing steam vents, bubbling mud pots, and an erupting geyser before heading into a lava tube and coming face-to-face with grizzlies. Three new bears will join the zoo in 2013 at the Medtronic Minnesota Trail, which features animals native to the state.

No. 17 Milwaukee County Zoological Gardens

Annual Visitors: 1,266,315

The 200-acre Milwaukee County Zoo cares so much about re-creating the wild that it places predators and prey in the same spaces. Antelopes, zebras, and ostriches coexist near lions, and Thompson’s gazelles stroll past cheetahs’ sight lines. But you won’t see any hunting. Strategically placed dry moats prevent would-be prey from becoming a big cat’s dinner. In recent years, the zoo welcomed a second African elephant and opened a new outdoor facility for its 17 bonobos, renovated its feline building, and completed a new indoor area for three hippos—including a new male named Happy, fresh from the National Zoo in D.C.

No. 18 Philadelphia Zoo

Annual Visitors: 1,265,229

The Philadelphia Zoo was the nation’s first, opened in 1874. Over the years, as its collection grew from 813 to more than 1,300 rare and endangered animals, the zoo has been the first to host the birth of orangutans, cheetahs, and giant otters—and the first to debut a children’s zoo in the Western Hemisphere. Now the zoo is in the process of creating the world’s first site-wide network of animal travel paths: animals will be able to roam greater distances outside of their habitats. In the meantime, monkeys and lemurs scamper overhead through the 700-foot Treetop Trail. Other trails, for orangutans, big cats, apes, bears, rhinos, hippos, giraffes, and zebras, are forthcoming.

No. 19 (tie) Albuquerque Biological Park, NM

Annual Visitors: 1,200,000

In 2010, two Tasmanian wombats came to the Albuquerque Zoo from the land down under and became the first in the country. They share the Australia exhibit with koalas and wallabies. Head over to the six-acre Africa exhibit when you’re ready for a look at chimpanzees, hippos, warthogs, cheetahs, elephants, red river hogs, and hyenas. A brand-new Amphibian and Reptile House will open at the end of Summer 2012, providing saltwater crocodiles, Komodo dragons, poison dart frogs, and their friends with new digs.

No. 19 (tie) San Diego Zoo Safari Park

Annual Visitors: 1,200,000

If you can’t make it to Africa, a trip through the San Diego Zoo Safari Park may be the next best thing. Sprawled over 1,800 acres, the park is home to more than 2,600 animals, many of which roam freely in open spaces that resemble their natural habitats. Hop aboard the Africa Tram to glimpse herds of giraffes, rhinos, Cape buffalo, and Grant’s gazelles. Want to get closer? Roll by on a Segway tour. Thrill-seekers can even soar above the African and Asian fields on a cool zipline more than two-thirds of a mile long. At the new Cheetah Run show, see the world’s fastest land mammal sprint from 0 to 70 miles per hour in just four seconds on a 330-foot track. You’ll be blown away—and not just from the wind the cheetah generates.